The aim of the current study is to evaluate under blinded conditions, both in a simulated environment and during helicopter flight, the effect of a rapid (within 20 minutes) exposure to altitude (4000 m asl) on physiological parameters and selected cognitive domains, in providers operating in helicopter emergency medical service (HEMS) exposed to hypobaric hypoxia or to hypobaric normoxia (H0: cognitive effects under hypobaric hypoxia = cognitive effects under hypobaric normoxia). Simulated environment will allow to control different factors. The parallelism between a study branch conducted in a simulated environment and another one conducted under a real-life condition will allow to evaluate the additive effects on additional stressor factors (processive and systemic ones).

• Simulation branch: each participant will take part in three research sessions: a familiarization session and two experimental sessions in simulation facility called terraXcube (test 1 and 2). On test 1 and test 2 each group will be exposed twice to the simulated altitude of 4000 m asl (under hypobaric hypoxia or hypobaric normoxia conditions) according to the randomization protocol. Participants will perform the neurocognitive tests three times on each of the two tests: before the ascent (TC0), after 5 min from the end of the ascent (TC1) and after around 30 min (TC2), to investigate European Union Aviation Safe Agency (EASA) proposed recommendations. After completing each neurocognitive test session, participants will be asked to rate their performance using a visual analogue scales (VAS). All participants will wear the vital parameters monitoring system during the entire duration of the tests inside the chamber, as well as the cerebral oxygen saturation (ScO2) sensor. Samples will be collected by saliva, urine and/or capillary blood. The same schedule is repeated in each test session.
• In-field branch: each participant will take part in three research sessions: a familiarization session and two experimental sessions during helicopter flights (test 1 and 2). On test 1 and test 2 each group will be exposed twice to the altitude of 4000 m (under hypobaric hypoxia or hypobaric normoxia conditions) according to the randomization protocol. Participants will perform the neurocognitive test two times on each test: before the ascent (TC0), after around 5 min from the end of the ascent (TC1). After completing each neurocognitive tests, participants will be asked to rate their performance using a visual analogue scales (VAS). All participants will wear the vital parameters monitoring system during the entire duration of the tests. Samples will be collected. The same schedule is planned in each test session.

Inclusion Criteria:

• members of emergency medical services (EMS) and search and rescue (SAR) services with an occupational licence;
• an age between 18 and 60 years;
• an American Society of Anaesthesiologists (ASA) physical status class I;
• provided informed and written consent;
• no current COVID 19 symptoms and temperature ≤ 37.5°on test days, not being tested positive for COVID-19, ideally COVID-19 vaccinated.

Exclusion Criteria:

• members under the age of 18 years;
• an ASA physical status class II or more;
• a medical history of psychiatric disorders and neurological diseases;
• previous high altitude pulmonary oedema (HAPE) or high altitude cerebral oedema (HACE) or severe acute mountain sickness (AMS) (defined as a Lake Louise Score (LLS) > 9) occurred at altitudes similar to the ones tested in the study;
• no informed consent;
• current COVID 19 symptoms, being tested positive for COVID-19 or symptoms and body temperature ≥ 37.5°on test days.